diff --git a/components/canvas/__tests__/compare-node.test.tsx b/components/canvas/__tests__/compare-node.test.tsx
new file mode 100644
index 0000000..93b8df6
--- /dev/null
+++ b/components/canvas/__tests__/compare-node.test.tsx
@@ -0,0 +1,160 @@
+import React from "react";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import { renderToStaticMarkup } from "react-dom/server";
+
+type StoreState = {
+  nodes: Array<{ id: string; type?: string; data?: unknown }>;
+  edges: Array<{
+    id: string;
+    source: string;
+    target: string;
+    className?: string;
+    targetHandle?: string;
+  }>;
+};
+
+const storeState: StoreState = {
+  nodes: [],
+  edges: [],
+};
+
+const compareSurfaceSpy = vi.fn();
+
+vi.mock("@xyflow/react", () => ({
+  Handle: () => null,
+  Position: { Left: "left", Right: "right" },
+  useStore: (selector: (state: StoreState) => unknown) => selector(storeState),
+}));
+
+vi.mock("../nodes/base-node-wrapper", () => ({
+  default: ({ children }: { children: React.ReactNode }) => <div>{children}</div>,
+}));
+
+vi.mock("../nodes/compare-surface", () => ({
+  default: (props: unknown) => {
+    compareSurfaceSpy(props);
+    return null;
+  },
+}));
+
+import CompareNode from "../nodes/compare-node";
+
+describe("CompareNode render preview inputs", () => {
+  beforeEach(() => {
+    storeState.nodes = [];
+    storeState.edges = [];
+    compareSurfaceSpy.mockReset();
+  });
+
+  it("passes previewInput to CompareSurface for a connected render node without final output", () => {
+    storeState.nodes = [
+      {
+        id: "image-1",
+        type: "image",
+        data: { url: "https://cdn.example.com/source.png" },
+      },
+      {
+        id: "render-1",
+        type: "render",
+        data: {},
+      },
+    ];
+    storeState.edges = [
+      { id: "edge-image-render", source: "image-1", target: "render-1" },
+      {
+        id: "edge-render-compare",
+        source: "render-1",
+        target: "compare-1",
+        targetHandle: "left",
+      },
+    ];
+
+    renderToStaticMarkup(
+      React.createElement(CompareNode, {
+        id: "compare-1",
+        data: { leftUrl: "https://cdn.example.com/render-output.png" },
+        selected: false,
+        dragging: false,
+        zIndex: 0,
+        isConnectable: true,
+        type: "compare",
+        xPos: 0,
+        yPos: 0,
+        width: 500,
+        height: 380,
+        sourcePosition: undefined,
+        targetPosition: undefined,
+        positionAbsoluteX: 0,
+        positionAbsoluteY: 0,
+      } as never),
+    );
+
+    expect(compareSurfaceSpy).toHaveBeenCalled();
+    const previewCall = compareSurfaceSpy.mock.calls.find(
+      ([props]) =>
+        Boolean(
+          (props as { previewInput?: { sourceUrl: string; steps: unknown[] } }).previewInput,
+        ),
+    );
+    expect(previewCall).toBeDefined();
+    expect(
+      (previewCall?.[0] as { previewInput?: { sourceUrl: string; steps: unknown[] } })
+        .previewInput,
+    ).toEqual({
+      sourceUrl: "https://cdn.example.com/source.png",
+      steps: [],
+    });
+  });
+
+  it("defaults render-backed compare inputs to preview mode even when a final render output exists", () => {
+    storeState.nodes = [
+      {
+        id: "image-1",
+        type: "image",
+        data: { url: "https://cdn.example.com/source.png" },
+      },
+      {
+        id: "render-1",
+        type: "render",
+        data: {
+          lastUploadUrl: "https://cdn.example.com/render-output.png",
+        },
+      },
+    ];
+    storeState.edges = [
+      { id: "edge-image-render", source: "image-1", target: "render-1" },
+      {
+        id: "edge-render-compare",
+        source: "render-1",
+        target: "compare-1",
+        targetHandle: "left",
+      },
+    ];
+
+    renderToStaticMarkup(
+      React.createElement(CompareNode, {
+        id: "compare-1",
+        data: { leftUrl: "https://cdn.example.com/render-output.png" },
+        selected: false,
+        dragging: false,
+        zIndex: 0,
+        isConnectable: true,
+        type: "compare",
+        xPos: 0,
+        yPos: 0,
+        width: 500,
+        height: 380,
+        sourcePosition: undefined,
+        targetPosition: undefined,
+        positionAbsoluteX: 0,
+        positionAbsoluteY: 0,
+      } as never),
+    );
+
+    expect(compareSurfaceSpy).toHaveBeenCalledTimes(1);
+    expect(compareSurfaceSpy.mock.calls[0]?.[0]).toMatchObject({
+      finalUrl: "https://cdn.example.com/render-output.png",
+      preferPreview: true,
+    });
+  });
+});
diff --git a/components/canvas/nodes/compare-node.tsx b/components/canvas/nodes/compare-node.tsx
index c533477..c69c918 100644
--- a/components/canvas/nodes/compare-node.tsx
+++ b/components/canvas/nodes/compare-node.tsx
@@ -148,7 +148,9 @@ export default function CompareNode({ id, data, selected, width }: NodeProps) {
     [incomingEdges, nodesById],
   );
   const shouldDefaultToPreview =
-    resolvedSides.left.isStaleRenderOutput || resolvedSides.right.isStaleRenderOutput;
+    hasConnectedRenderInput ||
+    resolvedSides.left.isStaleRenderOutput ||
+    resolvedSides.right.isStaleRenderOutput;
   const effectiveDisplayMode =
     manualDisplayMode ?? (shouldDefaultToPreview ? "preview" : "render");
   const previewNodeWidth = Math.max(240, Math.min(640, Math.round(width ?? 500)));
diff --git a/vitest.config.ts b/vitest.config.ts
index 654be67..141a59a 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -13,6 +13,7 @@ export default defineConfig({
       "tests/**/*.test.ts",
       "components/canvas/__tests__/canvas-helpers.test.ts",
       "components/canvas/__tests__/canvas-flow-reconciliation-helpers.test.ts",
+      "components/canvas/__tests__/compare-node.test.tsx",
       "components/canvas/__tests__/use-canvas-flow-reconciliation.test.ts",
       "components/canvas/__tests__/use-canvas-drop.test.tsx",
       "components/canvas/__tests__/use-canvas-node-interactions.test.tsx",